Surgeons performing minimally invasive surgery (MIS) manipulate surgical tools through the use of long slender instruments inserted through a small port, commonly in the patient's abdomen. To effectively perform these procedures, the surgeon must be able to accurately position and control the surgical instrument through manual or robotic manipulation. The instruments typically include a tool such as forceps or scissors coupled to a positioning apparatus that provides positioning flexibility. Presently available positioning apparatuses provide single segment articulation of the apparatus body in the form of rotational movement up to ninety degrees (90.degree.). Despite this flexibility, current instrumentation does not achieve the arbitrary orientation often required for complex surgical functions, such as suture placement.
The proper positioning of the surgical tool is complicated by several factors including the fact that the port in the patient's abdomen acts as a laterally restrictive pivot point for the body of the positioning apparatus. Additional factors limiting the effectiveness of MIS positioning apparatuses include the failure to provide articulation in more than one degree of freedom causing a lack of dexterity and the inability to approach a surgical site from an arbitrary orientation. Finally, the repeatability and controllability of traditional instruments, and therefore the fine manipulation skills of the surgeon, are further limited by the large actuation forces required by available actuators including push-pull cable, rotary shaft, and gear driven actuators having an excess number of linkages.
Historical MIS devices include the use of an articulated trunk mechanism, steerable channel, or a robot arm. However, each of these instrument positioning techniques have deficiencies that have prevented their widespread acceptance. Early devices were based upon steerable channels that could accommodate small flexible instruments. These channels allowed the instrument to be changed without negatively effecting the port, but were limited by their structural rigidity. Steerable channels are generally too compliant and unable to support sufficient loads.
Available robot arms and articulating trunks lack dexterity and precision. Specifically, articulating trunk mechanisms recently have included multiple hinged segments that provide bidirectional steering capability of up to 180.degree.. Steering is achieved with a series of hinge connected, equal length segments that operate together to define a single degree of freedom. The instrument can approach organs with arbitrary orientation but requires large actuation forces due to force magnification resulting from the instrument's kinematic design. Force magnification is a significant problem in dexterous surgical instrumentation as it restricts the ability of surgeons to perform fine manipulations during manual operation and significantly decreases load capacity.
Presently available trunk mechanisms also may provide rotation and actuation of a surgical tool connected to the end of the device via additional actuating assemblies. Unfortunately, as the force magnification increases with the square of the number of actuating links, the additional actuating assemblies negatively impact the ability of the surgeon to finely manipulate the device. Moreover, the rotation actuators of presently available trunk mechanisms are generally formed of a super elastic alloy which has a low life expectancy under high cyclic strains and which is adversely affected by large angles of deflection.
In view of the above, a need exists for an improved surgical instrument for positioning and operating a surgical tool. The instrument is desirably compact in design while including improved dexterity, fine motion capability, and load capacity when compared to traditional instruments.